1. Field of the Invention
The present invention relates to a metal sheet pile used for earth-retaining structures, fundamental structures, bank protection structures and a water cut-off walls in the civil engineering and construction fields. In particular, the present invention relates to the shape of a hat-type metal sheet pile.
2. Description of Background Art
It should be noted that FIG. 1 illustrates the present invention; however, this figure will also be used below for explanation purposes to identify the various elements of a typical metal sheet pile according to the background art. In addition, it should be noted that this discussion is directed to the present inventors' analysis of the background art and should not be construed to be an admission of prior art.
Referring to FIG. 1, a hat-type metal sheet pile of the present invention includes a flange 2, a pair of webs 3, 3, a pair of arms 4, 4 and a pair of joints 5, 5. Each of the pair of webs 3, 3 is connected to a respective end of the flange 2 so as to be line-symmetric with each other. Each of the pair of arms 4, 4 is connected at one thereof to the other end of the pair of webs 3, 3, respectively. The pair of arms 4, 4 is parallel to the flange 2. Furthermore, each of the pair of joints 5, 5 is connected to the other end of the pair of arms 4,4, respectively.
FIG. 1 shows a hat-type metal sheet pile where an effective width is B [mm], a height is H [mm], a web width is Bw [mm], a flange width is Bf [mm] and a flange thickness is t [mm]. The effective width B is defined as a distance between an interfitting center of a left joint 5 and an interfitting center of right joint 5. The interfitting center is defined as a center position of an area where a joint of one sheet pile and a joint of adjacent sheet pile overlap to interfit or interlock in the width direction of the sheet piles to form a pair of interfitted or interlocked joints.
A hat-type metal sheet pile is typically manufactured by a well-known method, i.e., rolling a hot bloom or slab of a piece of metal, typically steel, which has been heated to about 1250° C. in a furnace in advance. The rectangular hot piece of steel is passed a number of times using grooved rolls, which have a complicated shape to form a final cross-section. The metal sheet pile having the final cross-section is cut-off to make a predetermined length product when at a high temperature and is then cooled down. Bending and/or a warping caused during the rolling process is/are eliminated by using a roller straightener or a press straightener.
Typical metal sheet piles are U-type metal sheet piles and a hat-type metal sheet piles. Outlines of U-type metal sheet piles and hat-type metal shape piles are shown in outline form in FIGS. 8A and 8B, respectively. In order to form a metal wall having a certain length, a plurality of metal sheet piles are interlocked with each other by interfitting the joints 5. Therefore, it is economically advantageous to reduce the number of metal sheet piles by increasing the effective width B [mm] of a single metal sheet pile. However the effective width of metal sheet piles according to the background art has been 600 mm at the maximum.
Metal sheet piles are required to have a certain cross-sectional rigidity according to the intended use of the metal sheet pile. Cross-sectional rigidity is represented by a geometrical moment of inertia I [cm4/m] (=cross-sectional area×(distance to gravity-center axis of the metal sheet pile)2). Generally a geometrical moment of inertia I is more than 6,000 [cm4/m] (I>6,000 [cm4/m]). If the cross-sectional rigidity is the same between two kinds of metal sheet pile, a metal sheet pile having a weight per unit area W [kg/m2] smaller than the other metal sheet pile, i.e., the metal sheet pile having a better cross-section performance (I/W), is more economical than the other.
In view of the above, a metal sheet pile having more than a 700 mm effective width in order to reduce the number of sheet piles used and a metal sheet pile having a cross-sectional performance better than metal sheet piles according to the background art has been longed for.